Sildenafil, the active ingredient in Viagra, appears to help women who are suffering from moderate to severe menstrual cramps, according to a small study funded by the U.S. National Institutes of Health.

Researchers found that administering the medication vaginally provided nearly double the pain relief compared to a second group of women who received a placebo, or dummy drug.

The study focused on 25 women aged 18 to 35 who were suffering from primary dysmenorrhea (PD), the medical term for painful menstrual periods. PD accounts for 600 million lost work hours each year in the United States, according to background information from the study, which was published in the November issue of the journal Human Reproduction.

Ibuprofen and other nonsteroidal anti-inflammatory drugs are the current first-line treatment for menstrual cramps, but they do not work well for all women and can cause ulcers and kidney damage through prolonged use.

The researchers thought Viagra could dilate blood vessels and increase blood flow to the uterus, which might help relieve pain.

"It certainly makes sense for some women with PD that increasing blood flow to the area would increase oxygen to the pelvic tissues and potentially alleviate pain," said Dr. Jill Rabin, chief of ambulatory care, obstetrics and gynecology at the Long Island Jewish Medical Center in New Hyde Park, N.Y. Rabin was not involved with the new study.

Earlier studies tested oral use of Viagra to treat menstrual cramps, and found that the drug can ease pelvic pain. However, the side effects from oral use -- most often headaches -- were such that doctors ruled out routine use.

This was the first test of vaginal application of Viagra to try to treat menstrual cramps, the researchers said.

"The vagina is an effective route for drug administration intended mainly for local action because delivering medication in close proximity to the target organ decreases the incidence of side effects," they said.

Researchers from the Penn State College of Medicine worked with researchers from Croatia, who recruited 25 women at the Nova Gradiska General Hospital to receive either a 100-milligram sildenafil tablet or a placebo. The patients then rated their pain over a four-hour period.

Sildenafil administered vaginally was able to significantly alleviate menstrual pain, and without the side effects that come with oral use, the researchers said.

Women reported pain relief about double that of those who received a placebo, based on a scale used to measure their pain.

The researchers were not able, however, to explain why this occurred. Uterine blood flow increased from both sildenafil and the placebo, which did not match their initial theory.

Study co-author Dr. Richard Legro, of Penn State, said future studies will be required to verify the results of this small study and figure out how Viagra helps women with their cramps.

"If future studies confirm these findings, sildenafil may become a treatment option for patients with PD," Legro, a professor of public health sciences and obstetrics and gynecology, said in a university news release. "Since PD is a condition that most women suffer from and seek treatment for at some point in their lives, the quest for new medication is justified."

Rabin agreed that the idea shows great promise and should be further studied.

"It's always heartening when you have a tested medication like Viagra and someone thinks of a potential new use for it," she said.